Aqueous emulsions of various types of functionalized polyolefins have been used commercially since the late 1950s. Various methods for emulsifying low molecular weight polyolefins have been described by Force, U.S. Pat. No. 3,912,673, Von Bramer et al., "Polish Emulsion by Pressure Method," Soap and Chemical Specialties, December, 1966, and Nalley et al., U.S. Pat. No. 3,655,353.
Emulsions of functionalized polyolefins have a variety of uses. For example, emulsions of functionalized polyolefins are used in floor and car polishes, temporary metal coatings, corrugated and paper coatings, textile softener and lubricants, fiberglass sizing, and paper calendering lubricants and citrus fruit coatings. However, the use of low molecular weight polyolefins often yields coatings having insufficient hardness.
Thus, there is a need for improved emulsions having high molecular weight functionalized polyolefins. For example, in fiberglass sizing, a higher molecular weight would provide tougher and more abrasion-resistant coatings. The longer carbon chain lengths of a high molecular weight polymer would also provide greater "chain entanglements" in polymer/fiber composites. Such improved sizings could improve physical properties of polymer/fiber composites and allow lower cost polymers, such as polypropylene, to replace more expensive engineering plastics such as nylon or acrylonitrile-butadiene-styrene (ABS).
Various techniques have been described in recent years to satisfy this need for emulsified high molecular weight functionalized polyolefins. French patent No. 2,588,263, for example, describes a technique for emulsifying isotactic polyolefins of high molecular weight by dissolving the polymer with heat in an organic solvent that is immiscible in water, followed by dilution with water. Disadvantageously, however, this process requires the subsequent elimination of the solvent by extraction or by washing and drying. In addition to the burden of additional steps, the use of organic hydrocarbon solvents also brings safety concerns.
In another method for emulsifying high molecular weight polyolefins, Arpin et al., U.S. Pat. No. 5,389,440, describes a "two-step" direct pressure method whereby a high molecular weight polyolefin is first melt blended with a fatty acid to form a first mixture; a neutralizing base is then added to the first mixture along with an optional emulsifying agent to form a second mixture that is subsequently heated and cooled using a direct pressure process. However, this process is expensive, causes excessive degradation of the polyolefin, and results in relatively large particles (about 1-4 microns in diameter). Thus, there is a need for an improved process to emulsify high molecular weight functionalized polyolefins.